Carburetor Tuning Guide - Twisting Knobs On Holleys

Basic External Adjustments For Holley Carburetors

Some of the most popular Corvettes ever built were the chrome-bumper cars from '56 through '72. Within that model lineup, Holley carburetors saw service from '65 through '72. In some of those model years ('67 is a good example), Holleys were used exclusively. And in the aftermarket, Holley has offered-and still offers-hundreds of different carburetors targeted at different vehicle combinations. Plenty have been retrofitted to Corvettes of all model years, too.

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A majority of Holley carburetors were engineered as racing or high performance pieces. That meant they were (and still are) equipped with a number of easy-to-operate external tuning adjustments. For the performance freak, that's good news. You can easily fine-tune the carburetor to suit your application, and you can accomplish the basic tuning without going inside the carburetor. So far so good, but there's a bit of a hitch: If someone doesn't know what they're doing, they can just as easily turn a sweet running Corvette into a dud.

So which way do you turn the knobs, and which knobs do you turn? While not all of the adjustments involve actual "knobs," the basic external setup of a Holley isn't difficult. Everything can be accomplished at home with simple hand tools. For a closer look, check out the following. We're using a very common vacuum-secondary 3310 Holley as the example, and everything shown here applies to most factory installed Holleys, too.